606 KEPOET — 1889. 



ways of thinking and speaking about the phenomena of life. The error of the past 

 had been to believe that, although the heart resembled a pump, although digestion 

 could be imitated in the laboratory, and comparisons of vital with physical 

 processes could be used for illustration, it was always wrong to identify them. 

 But, inasmuch as it had been learned that sensation is propagated along a nerve 

 just as sound is propagated through the air, only with something like a tenth of the 

 velocity ; that the relations between the work done, the heat produced, and the fuel 

 used, can be investigated in the living body just as they are in the steam engine, it 

 now came to be felt that in other similar cases, what had been before regarded as 

 peculiarly vital might be understood on physical principles, and that for the future 

 the word * vital ' as distinctive of physiological processes might be abandoned 

 altogether. In looking back, we have no difficulty in seeing that the lines of 

 investigation which were then initiated by such men as Helmholtz, Ludwig, 

 Briicke, du Bois-Reymond, Bonders, Bernard, are those along which, during the 

 succeeding generation, the science of physiology advanced ; nor can anyone who 

 is acquainted with the literature of that time doubt that these leaders of physiolo- 

 gical thought knew that they were the beginners of a new epoch. But such an 

 epoch cannot occur again. We have adopted once for all the right, i.e. the 

 scientific method, and there is not the least possibility of our recurring to the 

 wrong. We have no new departure, no change of front in prospect ; but even 

 times which are not epochal have their tendencies, and I venture to submit to you, 

 that in physiology the tendency of the present time is characterised by the concen- 

 tration of the best efforts of the best minds on what I have already referred to as 

 elementary questions. The work of investigating the special functions of organs, 

 which during the last two decades has yielded such splendid results, is still 

 proceeding, and every year new ground is being broken and new and fruitful lines 

 of experimental inquiry are being opened up ; but the further the physiologist 

 advances in this work of analysis and differentiation, the more frequently does he 

 find his attention arrested by deeper questions relating to the essential endowments 

 of living matter, of which even the most highly differentiated functions of the 

 animal or plant organism are the outcome. In our science the order of progress 

 has been hitherto and will continue to be the reverse of the order of nature. 

 Nature begins with the elementary and ends with the complex (first the amoeba, 

 then the man). Our mode of investigation has to begin at the end. And this 

 not merely for the historical reason that the first stimulus to physiological inquiry 

 was man's reasonable desire to know himself, but because differentiation actually 

 involves simplification. For just as in manufactures it is the effect of division of 

 labour that less is required of each workman, so in an organism which is made up 

 of many organs, the function of each is simpler. 



Physiology, therefore, first studies man and the higher animals and proceeds to 

 the higher plants, then to invertebrates and cryptogams, ending where develop- 

 ment begins. From the beginning her aim has been to correlate function with 

 structure, at first roughly, afterwards, when, as I have explained, her methods of 

 observation became scientific, more and more accurately ; the principle being that 

 every appreciable difference of structure corresponds to a difference of function ; 

 and conversely that each endowment of a living organ must be explained, if 

 explained at all, as springing from its structure. 



It is not difficult to see whither this method must eventually lead us. For 

 inasmuch as function is more complicated than structure, the result of proceeding, 

 as physiology normally does, from structure to function, must inevitably be to bring 

 us face to face with functional differences which have no structural difference to 

 explain them. Thus, for example, if the physiologist undertakes to explain the 

 function of a highly differentiated organ like the eye, he finds that up to a certain 

 point, provided that he has the requisite knowledge of dioptrics, the method of cor- 

 relation guides him straight to his point. He can mentally or actually construct 

 an eye which will perform the functions of the real eye, in so far as the formation 

 of a real image of the field of vision on the retina is concerned, and will be able 

 thereby to understand how the retinal picture is transferred to the organ of con- 

 sciousness. Having arrived at this point he begins to correlate the known structure 



